Chinese authorities jailed the author of a history book critical of the ruling Communist Party for nearly two years on Friday, his lawyer said, calling the verdict "unconstitutional" as the nation marked Constitution Day.

China's constitution grants citizens rights to freedom of speech and the press but in practice authorities are intolerant of political dissent.

A court in central China's Jiangxi Province handed the sentence to Fu Zhibin, whose book "A History of Brainwashing", criticised "ideological control" in the country.

The author was sentenced to a year and 10 months in prison for "running an illegal business", his lawyer Zhang Zanning told AFP.

The charge is often used to jail activists.

Fu is the latest person to be jailed in a crackdown on critics of the Communist Party overseen by President Xi Jinping, which has seen hundreds detained and dozens sent to prison.

The court also sentence three others involved in the book's publication to between six months and one and a half years in jail, Zhang said.

The verdict came on China's second annual "Constitution Day", which sees officials vow to govern in accordance with the document and other laws.

But critics contend that the ruling party is effectively above the law and has never obeyed the constitution.

Zhang decried the verdict as "unconstitutional", adding: "this is clearly a thought crime, it's literary inquisition". The case suffered from a litany of procedural problems, he added.

The Communist Party tightly controls discussion of the constitution.

A court last year sentenced film director Shen Yongping, who made a documentary on the history of "constitutionalism" to a year in prison for "illegal business activities".

An editorial in the popular newspaper Southern Weekly on "constitutional government" was censored in 2013, sparking small-scale press freedom protests.

Last week, China jailed three activists who helped organise the demonstrations, with one, Guo Feixiong, given a six-year sentence.